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Conventional electrolytes made by mixing simple Mg2+ salts and aprotic solvents, analogous to those in Li-ion batteries, are incompatible with Mg anodes because Mg metal readily reacts with such el...

The bis(fluorosulfonyl)imide anion N(SO2F)2 − (i.e., FSI−) (also referred to as bis(fluorosulfonyl)amide (i.e., FSA−) and imidodi(sulphuryl fluoride)) has attracted tremendous interest in recent years for its utility in both lithium salts and ionic liquids for battery electrolyte applications. To facilitate the understanding of the characteristics of this anion, crystal structures are reported here for the uncoordinated anion in LiFSI-based solvates with cryptand CRYPT-222 and tetraglyme (G4). These crystalline solvates were analyzed by Raman spectroscopy to aid in assigning the Raman bands to the modes of ion coordination found in liquid electrolytes. These structures, as well as a thorough review of other relevant crystallographic data, provide insights into the rather remarkable properties of the FSI− anion with regard to solvate formation and electrolyte properties.

The lithium-sulfur (Li-S) battery is a very promising candidate for the next generation of energy storage systems required for electrical vehicles and grid energy storage applications due to its very high theoretical specific energy (2500 W h kg−1). However, low Coulombic efficiency (CE) during repeated Li metal plating/stripping has severely limited the practical application of rechargeable Li-S batteries. In this work, a new electrolyte system based on a high concentration of LiNO3 in diglyme (G2) solvent is developed which enables an exceptionally high CE for Li metal plating/stripping and thus high stability of the Li anode in the sulfur-containing electrolyte. The tailoring of electrolyte properties for the Li anode has proven to be a highly successful strategy for improving the capacity retention and cycle life of Li-S batteries. This electrolyte provides a CE of greater than 99% for over 200 cycles of Li plating/stripping. In contrast, the Li anode cycles for less than 35 cycles (with a high CE) in the state-of-the-art 1 M LiTFSI + 0.3 M LiNO3 in 1,3-dioxolane:1,2-dimethoxyethane (DOL:DME) electrolyte under the same conditions. The stable Li anode enabled by the new electrolyte may accelerate the applications of high energy density Li-S batteries in both electrical vehicles and large-scale grid energy storage markets.

Li–S batteries have been extensively studied using rigid carbon as the host for sulfur encapsulation, but improving the properties with a reduced electrolyte amount remains a significant challenge. This is critical for achieving high energy density. Here, we developed a soft PEO10LiTFSI polymer swellable gel as a nanoscale reservoir to trap the polysulfides under lean electrolyte conditions. The PEO10LiTFSI gel immobilizes the electrolyte and confines polysulfides within the ion conducting phase. The Li–S cell with a much lower electrolyte to sulfur ratio (E/S) of 4 gE/gS (3.3 mLE/gS) could deliver a capacity of 1200 mA h/g, 4.6 mA h/cm2, and good cycle life. The accumulation of polysulfide reduction products, such as Li2S, on the cathode, is identified as the potential mechanism for capacity fading under lean electrolyte conditions.

Rechargeable batteries based upon sodium (Na+) cations are at the core of many new battery chemistries beyond Li-ion batteries. Rather than using carbon or alloy-based anodes, the direct utilization of solid sodium metal as an anode would be highly advantageous, but its use has been highly problematic due to its high reactivity. In this work, it is demonstrated that, by tailoring the electrolyte formulation, solid Na metal can be electrochemically plated/stripped at ambient temperature with high efficiency (>99%) on both copper and inexpensive aluminum current collectors thereby enabling a shift in focus to new battery chemical couples based upon Na metal operating at ambient temperature. These highly concentrated electrolytes have enabled excellent cycling stability of Na metal batteries using Na metal anode and Na3V2(PO4)3 cathode at high rates with very high efficiency.

Anode-free rechargeable lithium (Li) batteries (AFLBs) are phenomenal energy storage systems due to their significantly increased energy density and reduced cost relative to Li-ion batteries, as well as ease of assembly because of the absence of an active (reactive) anode material. However, significant challenges, including Li dendrite growth and low cycling Coulombic efficiency (CE), have prevented their practical implementation. Here, an anode-free rechargeable lithium battery based on a Cu||LiFePO4 cell structure with an extremely high CE (>99.8%) is reported for the first time. This results from the utilization of both an exceptionally stable electrolyte and optimized charge/discharge protocols, which minimize the corrosion of the in situly formed Li metal anode.

The composition of the lithium cation (Li(+)) solvation shell in mixed linear and cyclic carbonate-based electrolytes has been re-examined using Born-Oppenheimer molecular dynamics (BOMD) as a function of salt concentration and cluster calculations with ethylene carbonate:dimethyl carbonate (EC:DMC)-LiPF6 as a model system. A coordination preference for EC over DMC to a Li(+) was found at low salt concentrations, while a slightly higher preference for DMC over EC was found at high salt concentrations. Analysis of the relative binding energies of the (EC)n(DMC)m-Li(+) and (EC)n(DMC)m-LiPF6 solvates in the gas-phase and for an implicit solvent (as a function of the solvent dielectric constant) indicated that the DMC-containing Li(+) solvates were stabilized relative to (EC4)-Li(+) and (EC)3-LiPF6 by immersing them in the implicit solvent. Such stabilization was more pronounced in the implicit solvents with a high dielectric constant. Results from previous Raman and IR experiments were reanalyzed and reconciled by correcting them for changes of the Raman activities, IR intensities and band shifts for the solvents which occur upon Li(+) coordination. After these correction factors were applied to the results of BOMD simulations, the composition of the Li(+) solvation shell from the BOMD simulations was found to agree well with the solvation numbers extracted from Raman experiments. Finally, the mechanism of the Li(+) diffusion in the dilute (EC:DMC)LiPF6 mixed solvent electrolyte was studied using the BOMD simulations.

Hard carbon nanoparticles (HCNP) were synthesized by the pyrolysis of a polyaniline precursor. The measured Na+ cation diffusion coefficient (10−13–10−15 cm2 s−1) in the HCNP obtained at 1150 °C is two orders of magnitude lower than that of Li+ in graphite (10−10–10−13 cm2 s−1), indicating that reducing the carbon particle size is very important for improving electrochemical performance. These measurements also enable a clear visualization of the stepwise reaction phases and rate changes which occur throughout the insertion/extraction processes in HCNP, The electrochemical measurements also show that the nano-sized HCNP obtained at 1150 °C exhibited higher practical capacity at voltages lower than 1.2 V (vs. Na/Na+), as well as a prolonged cycling stability, which is attributed to an optimum spacing of 0.366 nm between the graphitic layers and the nano particular size resulting in a low-barrier Na+ cation insertion. These results suggest that HCNP is a very promising high-capacity/stability anode for low cost sodium-ion batteries (SIBs).

Lithium–sulfur (Li–S) batteries are regarded as one of the most promising candidates for next generation energy storage. To realize their practical application, however, a high S active material loading is essential. The binder material used for the cathode is therefore crucial as this is a key determinant of the bonding interactions between the active material (S) and electronic conducting support (C), as well as the maintenance of intimate contact between the electrode materials and current collector. Here, we investigated the application of polyamidoamine (PAMAM) dendrimers as functional binders in Li–S batteries. Utilizing the high degree of surface functionalities, interior porosities, and polarity of the PAMAM dendrimers, it is demonstrated that high S loadings (>4 mg cm−2) can be easily achieved using simple processing methods. An exceptional electrochemical cycling performance was obtained as compared to cathodes with conventional linear polymeric binders such as carboxymethyl cellulose (CMC) and styrene–butadiene rubber (SBR), which was attributed to better interfacial interactions between the dendrimers and the C/S composite materials, as well as better electrolyte wetting due to the dendrimer spherical molecular, porous architectures. Furthermore, the dendrimer-based binders also physically and chemically trapped the polar polysulfides, thus demonstrating the significant utility of this new nanosized binder architecture.

Details of the lithium (Li+), sodium (Na+), magnesium (Mg2+), and zinc (Zn2+) cation coordination and electrolyte transport properties are examined using molecular dynamics (MD) simulations for the N-butyl-N-methylpyrrolidinium bis(trifluoromethansulfonyl)imide (pyr14TFSI) ionic liquid (IL) doped with LiTFSI, NaTFSI, Mg(TFSI)2, and Zn(TFSI)2 salts. MD simulations are performed as a function of temperature using a polarizable force field (APPLE&P) that yields the Li+, Na+, Mg2+, and Zn2+ cation binding energies to the TFSI- anions in excellent agreement with quantum chemistry results. At 333 K, 4.7-4.8 TFSI- oxygen atoms from approximately three TFSI- anions coordinate Li+ and Na+, while Zn2+ and Mg2+ cations are instead coordinated by approximately six TFSI- oxygen atoms. Significant Na+ coordination with the fluorine atoms of the TFSI- anions is observed, unlike for Li+, Mg2+ and Zn2+. The cation-TFSI- binding motifs and the propensity of the salts to form large aggregates are temperature dependent with opposite trends noted for the electrolytes containing the Li and Na salts vs Mg salts. The MD simulations accurately predicted electrolyte transport properties including ionic conductivity, viscosity, and self-diffusion coefficients. A connection between the metal cation coordination, transport properties, and transport mechanisms is established for the different cations. The much longer cation-anion residence times for the divalent Zn2+- and Mg2+-containing electrolytes, as compared to those with monovalent Na+ and Li+, indicate the significantly slower desolvation kinetics of the divalent salts and the dominance of the vehicular cation transport mechanism relative to the anion exchange mechanism.

Residual water (H2O) presents in nonaqueous electrolytes has been widely regarded as a detrimental factor for lithium (Li) batteries. This is because H2O is highly reactive with the commonly used LiPF6 salt leading to the formation of HF which subsequently corrodes battery materials. In this work, we demonstrate that a controlled trace-amount of H2O (25–50 ppm) can be an effective electrolyte additive for achieving dendrite-free Li metal deposition in LiPF6-based electrolytes, while avoid detrimental effects. Detailed analyses revealed that the trace amount of HF derived from the decomposition reaction of LiPF6 with H2O is electrochemically reduced during the initial Li deposition process to form a uniform and dense LiF-rich solid electrolyte interphase (SEI) layer on the surface of the substrate. This LiF-rich SEI layer leads to a uniform distribution of the electric field on the substrate surface thereby enabling uniform and dendrite-free Li deposition. Meanwhile, the detrimental effect of HF on the other cell components is diminished due to the consumption of the HF in the LiF formation process. Microscopic analysis reveals that the as-deposited, dendrite-free Li films exhibit a self-aligned and highly-compact Li nanorod structure which is consistent with a vivid blue color due to structural coloration. These findings clearly demonstrate a novel approach to control the nucleation and grow processes of Li metal films using a well-controlled, trace-amount of H2O, as well as illuminate the effect of H2O on other electrodeposition processes.

Nonaqueous redox flow batteries hold the promise of achieving higher energy density because of the broader voltage window than aqueous systems, but their current performance is limited by low redox material concentration, cell efficiency, cycling stability, and current density. We report a new nonaqueous all-organic flow battery based on high concentrations of redox materials, which shows significant, comprehensive improvement in flow battery performance. A mechanistic electron spin resonance study reveals that the choice of supporting electrolytes greatly affects the chemical stability of the charged radical species especially the negative side radical anion, which dominates the cycling stability of these flow cells. This finding not only increases our fundamental understanding of performance degradation in flow batteries using radical-based redox species, but also offers insights toward rational electrolyte optimization for improving the cycling stability of these flow batteries.

Crystal structures have been determined for both LiBF4 and HBF4 solvates: (acetonitrile)(2):LiBF4, (ethylene glycol diethyl ether)(1):LiBF4, (diethylene glycol diethyl ether)(1):LiBF4, (tetrahydrofuran)(1):LiBF4, (methyl methoxyacetate)(1):LiBF4, (succinonitrile)(1):LiBF4, (N,N,N',N '',N ''-pentamethyldiethylenetriamine)(1):HBF4, (N,N,N',N'-tetramethylethylenediamine)(3/2):HBF4, and (phenanthroline)(2):HBF4. These, as well as other known LiBF4 solvate structures, have been characterized by Raman vibrational spectroscopy to unambiguously assign the anion Raman band positions to specific forms of BF4-center dot center dot center dot Li+ cation coordination. In addition, complementary DFT calculations of BF4-center dot center dot center dot Li+ cation complexes have provided additional insight into the challenges associated with accurately interpreting the anion interactions from experimental Raman spectra. This information provides a crucial tool for the characterization of the ionic association interactions within electrolytes.

An operando electrochemical stage for the transmission electron microscope has been configured to form a “Li battery” that is used to quantify the electrochemical processes that occur at the anode during charge/discharge cycling. Of particular importance for these observations is the identification of an image contrast reversal that originates from solid Li being less dense than the surrounding liquid electrolyte and electrode surface. This contrast allows Li to be identified from Li-containing compounds that make up the solid-electrolyte interphase (SEI) layer. By correlating images showing the sequence of Li electrodeposition and the evolution of the SEI layer with simultaneously acquired and calibrated cyclic voltammograms, electrodeposition, and electrolyte breakdown processes can be quantified directly on the nanoscale. This approach opens up intriguing new possibilities to rapidly visualize and test the electrochemical performance of a wide range of electrode/electrolyte combinations for next generation battery systems.

aElectrochemistry Branch, U.S. Army Research Laboratory, Adelphi, Maryland 20783, USA bIonic Liquids & Electrolytes for Energy Technologies (ILEET) Laboratory, Department of Chemical & Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina 27695, USA cSchool of Environmental Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju 500-712, Republic of Korea dElectrochemical Materials & Systems (EMS) Group, Energy & Environment Directorate, Pacific Northwest National Laboratory (PNNL), Richland, Washington 99352, USA

Combined computational/Raman spectroscopic analyses of ethylene carbonate (EC) and propylene carbonate (PC) solvation interactions with lithium salts are reported. It is proposed that previously reported Raman analyses of (EC)n–LiX mixtures have utilized faulty assumptions. In the present studies, density functional theory (DFT) calculations have provided corrections in terms of both the scaling factors for the solvent's Raman band intensity variations and information about band overlap. By accounting for these factors, the solvation numbers obtained from two different EC solvent bands are in excellent agreement with one another. The same analysis for PC, however, was found to be quite challenging. Commercially available PC is a racemic mixture of (S)- and (R)-PC isomers. Based upon the quantum chemistry calculations, each of these solvent isomers may exist as multiple conformers due to a low energy barrier for ring inversion, making deconvolution of the Raman bands daunting and inherently prone to significant error. Thus, Raman spectroscopy is able to accurately determine the extent of the EC…Li+ cation solvation interactions using the provided methodology, but a similar analysis of PC…Li+ cation solvation results in a significant underestimation of the actual solvation numbers.

Only limited information is available regarding the manner in which cyclic carbonate and ester solvents coordinate Li+ cations in electrolyte solutions for lithium batteries. One approach to gleaning significant insight into these interactions is to examine crystalline solvate structures. To this end, eight new solvate structures are reported with ethylene carbonate, γ-butyrolactone, and γ-valerolactone: (EC)3:LiClO4, (EC)2:LiClO4, (EC)2:LiBF4, (GBL)4:LiPF6, (GBL)1:LiClO4, (GVL)1:LiClO4, (GBL)1:LiBF4, and (GBL)1:LiCF3SO3. The crystal structure of (EC)1:LiCF3SO3 is also re-reported for comparison. These structures enable the factors that govern the manner in which the ions are coordinated and the ion/solvent packing—in the solid-state—to be scrutinized in detail.

Li-ion batteries (LIB) have been successfully commercialized after the identification of ethylene-carbonate (EC)-containing electrolyte that can form a stable solid electrolyte interphase (SEI) on carbon anode surface to passivate further side reactions but still enable the transportation of the Li+ cation. These electrolytes are still utilized, with only minor changes, after three decades. However, the long-term cycling of LIB leads to continuous consumption of electrolyte and growth of SEI layer on the electrode surface, which limits the battery’s life and performance. Herein, a new anode protection mechanism is reported in which, upon changing of the cell potential, the electrolyte components at the electrode–electrolyte interface reorganize reversibly to form a transient protective surface layers on the anode. This layer will disappear after the applied potential is removed so that no permanent SEI layer is required to protect the carbon anode. This phenomenon minimizes the need for a permanent SEI la...

In the present work, a number of wide operating temperature range electrolyte formulations that contain methyl butyrate (MB) and various additives have been investigated in Li-ion cells consisting of Conoco Phillips A12 graphite anodes and Toda HE5050 Li1.2Ni0.15Co0.10Mn0.55O2 cathodes. In an attempt to improve the nature of the solid electrolyte interphase (SEI) and/or cathode electrolyte interface (CEI) of these systems, a number of electrolyte additives were investigated, including lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), 4,5-dicyano-2-(trifluoromethyl) imidazole (LiTDI), lithium tetrafluoroborate (LiBF4), and di-t-butylpyrocarbonate (DBPC). In summary, improved performance at low temperature power capability was observed for many of the methyl butyrate formulations, with the most dramatic improvement being observed for 1.20M LiPF6 in EC+EMC+MB (20:20:60 v/v %) + 0.10M LiDFOB. In addition, all of the methyl butyrate-based electrolytes studied resulted in improved rate capability compared to cells with the all carbonate-based baseline formulation at low temperature. It was also determined that at low temperatures that the cathode kinetics govern the rate capability, being the rate determining electrode.

Lithium 4,5-dicyano-1,2,3-triazolate (LiDCTA) and lithium 2-trifluoromethyl-4,5-dicyanoimidazole (LiTDI) are two salts proposed for lithium battery electrolyte applications, but little is known about the manner in which the DCTA– and TDI– anions coordinate Li+ cations. To explore this in depth, crystal structures are reported here for two solvates with LiDCTA—(G2)1:LiDCTA and (G1)1:LiDCTA—with diglyme and monoglyme, respectively; and seven solvates with LiTDI—(G1)2:LiTDI, (G2)2:LiTDI, (G3)1:LiTDI, (THF)1:LiTDI, (EC)1:LiTDI, (PC)1:LiTDI, and (DMC)1/2:LiTDI—with monoglyme, diglyme, triglyme, tetrahydrofuran, ethylene carbonate, propylene carbonate, and dimethyl carbonate, respectively. These latter solvate structures are compared with the previously reported acetonitrile (AN)2:LiTDI structure. The solvates indicate that the LiTDI salt is much less associated than the LiDCTA salt and that the ions in LiTDI, when aggregated in solvates, have a very similar TDI–···Li+ cation mode of coordination through both t...

Fluorine-free lithium battery electrolytes have been prepared from lithium salts with nitrile based anions, LiB(CN)4 or LiDCTA, dissolved in PEGDME or PC. After soaked into electrospun PAN membranes the resulting electrolytes were tested for physical and electrochemical properties and compared with reference PAN electrolytes containing LiPF6 or LiTFSI. The fluorine-free electrolytes were successfully cycled in Li/LiFePO4 cells at room temperature with up to 98% Coulombic efficiency. Small and qualitatively different effects were observed with the addition of Al 2O3 particles to the PAN membranes, which could be of importance for long-term performance. However, for fluorine-free electrolytes to be truly competitive, the relatively low anodic stability and elevated temperature performance must first of all be improved by a change of solvent - or addition of co-solvents. Further work in this direction is encouraged by the strong influence of the solvent (PC or PEGDME) on the properties of the LiDCTA electrolytes demonstrated in this work. © 2013 Elsevier B.V. All rights reserved.

Highly concentrated electrolytes containing carbonate solvents with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) have been investigated to determine the influence of eliminating bulk solvent (i.e., uncoordinated to a Li+ cation) on electrolyte properties. The phase behavior of ethylene carbonate (EC)–LiTFSI mixtures indicates that two crystalline solvates form—(EC)3:LiTFSI and (EC)1:LiTFSI. Crystal structures for these were determined to obtain insight into the ion and solvent coordination. Between these compositions, however, a crystallinity gap exists. A Raman spectroscopic analysis of the EC solvent bands for the 3–1 and 2–1 EC–LiTFSI liquid electrolytes indicates that ∼86 and 95%, respectively, of the solvent is coordinated to the Li+ cations. This extensive coordination results in significantly improved anodic oxidation and thermal stabilities as compared with more dilute (i.e., 1 M) electrolytes. Further, while dilute EC–LiTFSI electrolytes extensively corrode the Al current collector at high potential, the concentrated electrolytes do not. A new mechanism for electrolyte corrosion of Al in Li-ion batteries is proposed to explain this. Although the ionic conductivity of concentrated EC–LiTFSI electrolytes is somewhat low relative to the current state-of-the-art electrolyte formulations used in commercial Li-ion batteries, using an EC–diethyl carbonate (DEC) mixed solvent instead of pure EC markedly improves the conductivity.

Electrolytes with the salt lithium bis(fluorosulfonyl)imide (LiFSI) have been evaluated relative to comparable electrolytes with other lithium salts. Acetonitrile (AN) has been used as a model electrolyte solvent. The information obtained from the thermal phase behavior, solvation/ionic association interactions, quantum chemical (QC) calculations and molecular dynamics (MD) simulations (with an APPLE&P many-body polarizable force field for the LiFSI salt) of the (AN)n-LiFSI mixtures provides detailed insight into the coordination interactions of the FSI- anions and the wide variability noted in the electrolyte transport property (i.e., viscosity and ionic conductivity).

A highly effective method has been developed for the simple extraction of lignin from lignocellulosic biomass using a potentially inexpensive protic ionic liquid (PIL). After the lignin-extraction step, the PIL is easily recovered using distillation leaving the separated lignin and cellulose-rich residues available for further processing. Biopolymer solubility tests indicate that increasing the xylan (i.e., hemicellulose) solubility in the PIL results in greater fiber disruption/penetration, which significantly enhances the effectiveness of the lignin extraction.

The choice of non-solvent has a dramatic influence on the morphology/crystallinity of regenerated cellulose obtained following ionic liquid (IL) dissolution. This, in turn, greatly impacts the enzymatic digestibility of the cellulose. The use of ethanol (in contrast to water) provides a high surface-area, amorphous regenerated material ideal for hydrolysis—ethanol is also more facile to separate from the IL than water during the recovery/recycling process for the IL.

Presented here are data describing the phase behavior and solvation of lithium trifluoromethanesulfonate (LiCF3SO3) in propylene carbonate (PC). Data obtained from differential scanning calorimetry (DSC) and Raman spectroscopy of sample mixtures are correlated to enhance understanding of solvent-salt associations. A phase diagram will display the behavior of the solvent-salt interactions. The binary phase diagram constructed from thermal data acquired by DSC analyses indicated only glass transition temperatures for all mixtures of PC-LiCF3SO3 tested. Raman spectroscopy is applied to probe the liquid electrolyte and discover solvent-salt associations in solution. Results indicate that mixtures of PC-LiCF3SO3 do not readily form solvent-separated ion pairs but rather tend toward contact ion pair and more aggregated solvates. Overall, this study provided some insight into electrolyte solvation of these model battery electrolyte species.

Batteries are one of the most impactful inventions humankind has ever developed. Lithium-ion energy cells represent a significant advance in battery technology. Electrolytes used in batteries are still not well understood in terms of solution structure. We investigate electrolyte solvate structure with the aid of differential scanning calorimetry, Raman spectroscopy, and X-ray diffraction. Here is a report on the solvate structure(s) present in mixtures of propylene carbonate (PC) and lithium trifluoromethanesulfonate (LiTf). Mixtures of racemic PC with LiTf form glasses whereas enantiomerically pure PC, both R and S isomers, forms mixtures with more complex phase behavior. At concentrations approaching a 1:1 molar ratio of solvent to salt, a solvate that melts at ~150 °C was detected. A crystal of the 1:1 solvate of the R-(+)-PC:LiTf was successfully grown and analyzed by X-ray diffraction. This solvate has an aggregated structure where the Li+ cations are tetrahedrally coordinated. Three directions of coordination come from Tf– anions acting as a bridging ligand between three different Li+ cations and the 4th direction of coordination comes from the carbonyl oxygen of the solvent molecule.

Lithium difluoro(oxalato)borate (LiDFOB) and lithium bis(oxalato)borate (LiBOB) have emerged as superior additives for the formation of favorable passivation layers on active electrodes. In this study, we systematically investigate the thermal phase behavior and electrochemical/physicochemical properties of LiBF4, LiDFOB and LiBOB mixtures with the cyclic carbonate ethylene carbonate (EC) and ester γ-butyrolactone (GBL). Raman spectroscopy was used to determine the degree of solvation that is present in the liquid electrolytes, which may then be directly correlated to the bulk conductivity of the mixtures.

Phase diagrams have been prepared for cyclic carbonate and ester mixtures with LiTFSI and LiPF6. A Raman analysis of the mixtures enables the determination of the degree of solvation of the Li+ cations. Key insight into the link between solvent structure and solvation is obtained. It was discovered that the solvent polarity parameters are poor indicators of the molecular-level solvation interactions.

Lithium difluoro(oxalato)borate (LiDFOB) is a relatively new salt designed for battery electrolyte usage. Limited information is currently available, however, regarding the ionic interactions of this salt (i.e., solvate formation) when it is dissolved in aprotic solvents. Vibrational spectroscopy is a particularly useful tool for identifying these interactions, but only if the vibrational bands can be correctly linked to specific forms of anion coordination. Single crystal structures of LiDFOB solvates have therefore been used to both explore the DFOB-center dot center dot center dot Li+ cation coordination interactions and serve as unambiguous models for the assignment of the Raman vibrational bands. The solvate crystal structures determined indude (monoglyme)(2):LiDFOB, (1,2-diethoxyethane)(3/2):LiDFOB, (acetonitrile)(3):LiDFOB, (acetonitrile)(1):LiDFOB, (dimethyl carbonate)(3/2):LiDFOB, (succinonitrile)(1):LiDFOB, (adiponitrile)(1):LiDFOB, (PMDETA)(1):LiDFOB, (CRYPT-222)(2/3):LiDFOB, and (propylene carbonate)(1):LiDFOB. DFT calculations have been incorporated to provide additional insight into the origin (i.e., vibrational modes) of the Raman vibrational bands to aid in the interpretation of the experimental analysis.

aIonic Liquids & Electrolytes for Energy Technologies (ILEET) Laboratory, Department of Chemical & Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina 27695, USA bElectrochemistry Branch, U.S. Army Research Laboratory, Adelphi, Maryland 20783, USA cSchool of Environmental Science & Engineering, Gwangju Institute of Science and Technology (GIST), 123 Cheomdan-Gwangiro, Buk-gu, Gwangju 500-712, Korea

The Li plating morphology and Coulombic efficiency of Li deposition are critical for the safety and cycleability of Li metal batteries. Almost all the factors that lead to significant dendritic growth also lead to a lower CE and vice versa. Various factors that affect both the Li plating morphology and Coulombic efficiency of Li cycling will be discussed in this chapter.

The Li dendrite growth and corrosion of Li anode during the Li deposition process are critical issues for the battery safety and long term cyclability of Li metal batteries. In this chapter, we will first review various instruments/tools that are critical for the characterization of Li dendrite growth/stripping processes and analysis on the composition of the surface films formed during Li deposition process, and then the general models of the Li deposition, especially Li dendrite formation and grow processes will be discussed.

Li metal is an ideal anode to replace carbon based anode used in the state of the art Li-ion batteries. It is also widely used in Li-S and Li-air batteries. Although the use of Li metal anodes in these batteries has been limited by Li dendrite growth and the low CE of Li cycling, the stability of Li metal anodes is much different when used in different types of Li metal batteries and will be discussed separately in this chapter.